Data from: Invariant antagonistic network structure despite high spatial and temporal turnover of interactions

Recent work has suggested that emergent ecological network structure exhibits very little spatial or temporal variance despite changes in community composition. However, the changes in network interactions associated with turnover in community composition have seldom been assessed. Here we examine whether changes in ecological networks are best detected by standard emergent network metrics or by assessing internal network changes (i.e. interaction and composition turnover). To eliminate possible spatial or phylogenetic effects, that in large-scale studies may obscure mechanisms structuring networks and interactions, we sampled multiple antagonistic (plant-herbivore) networks for a single diverse plant family (the Restionaceae) in the hyperdiverse Cape Floristic Region. These are the first plant-herbivore networks constructed for this global biodiversity hotspot. We found invariant emergent network structure despite considerable changes in insect and plant composition across communities over time and space. In contrast, there was high interaction turnover between networks. Seasonally, this was driven by turnover in insect species and insect host switching. Spatially, this was driven by simultaneous turnover in plant and insect species, suggesting that many insects are host specific or that both groups exhibit parallel responses to environmental gradients. Spatial interaction turnover was also driven by turnover in plants, showing that many insects can utilise multiple (possibly closely related) hosts and this may create divergent selection gradients that promote insect speciation. Thus we show highly variable interaction fidelity, despite invariant emergent network structure. We suggest that evaluating internal network changes may be more effective at elucidating the processes structuring networks, and many fine-scale changes may be obscured when only calculating emergent network metrics.

近期研究表明，尽管群落组成发生改变，涌现生态网络（emergent ecological network）结构仅存在极微弱的空间或时间变异。然而，与群落组成周转相关的网络相互作用变化，却极少得到评估。为消除大型研究中可能掩盖网络与相互作用构建机制的空间或系统发育效应，我们针对物种超多样化的开普植物区（Cape Floristic Region）内的单一多样化植物科——帚灯草科（Restionaceae），对多个拮抗（plant-herbivore）网络开展采样。这是首个针对该全球生物多样性热点地区构建的植物-植食性昆虫网络。我们发现，尽管不同群落中的昆虫与植物组成随时间和空间发生显著变化，但涌现网络结构始终保持恒定。与之形成鲜明对比的是，不同网络间的相互作用周转程度极高。在季节尺度上，该周转由昆虫物种周转与昆虫寄主转换共同驱动；在空间尺度上，则由植物与昆虫物种的同步周转所主导，这提示多数昆虫具有寄主专化性，或两类群对环境梯度呈现平行响应。空间尺度的相互作用周转还受植物物种周转的影响，表明许多昆虫可利用多种（可能为近缘的）寄主，这一过程或可形成分化选择梯度，进而推动昆虫物种形成。综上，我们证实尽管涌现网络结构恒定，但相互作用保真度存在高度变异。我们提出，评估网络内部的变化或许更有助于阐明构建网络的生态学过程；若仅计算涌现网络指标，诸多精细尺度的变化可能被掩盖。